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JunosOperating system · Juniper

CVE-2021-0275

HIGH · 8.8 CVSS v3.1 Published 2021-04-22
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
95/100
Remediation priority · Urgent
Remotely reachable No privileges

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A Cross-site Scripting (XSS) vulnerability in J-Web on Juniper Networks Junos OS allows an attacker to target another user's session thereby gaining access to the users session. The other user session must be active for the attack to succeed. Once successful, the attacker has the same privileges as the user. If the user has root privileges, the attacker may be able to gain full control of the device. This issue affects: Juniper Networks Junos OS: 12.3 versions prior to 12.3R12-S15 on EX Series; 12.3X48 versions prior to 12.3X48-D95 on SRX Series; 15.1 versions prior to 15.1R7-S6 on EX Series; 15.1X49 versions prior to 15.1X49-D200 on SRX Series; 16.1 versions prior to 16.1R7-S7; 16.2 versions prior to 16.2R2-S11, 16.2R3; 17.1 versions prior to 17.1R2-S11, 17.1R3-S2; 17.2 versions prior to 17.2R3-S3; 17.3 versions prior to 17.3R2-S5, 17.3R3-S7; 17.4 versions prior to 17.4R2-S9, 17.4R3; 18.1 versions prior to 18.1R3-S9; 18.2 versions prior to 18.2R2-S7, 18.2R3-S3; 18.3 versions prior to 18.3R1-S7, 18.3R2-S3, 18.3R3-S1; 18.4 versions prior to 18.4R1-S6, 18.4R2-S4, 18.4R3; 19.1 versions prior to 19.1R2-S1, 19.1R3; 19.2 versions prior to 19.2R1-S3, 19.2R2; 19.3 versions prior to 19.3R2.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Cross-site Scripting (XSS) vulnerability in J-Web interface of Juniper Networks Junos OS allows authenticated attackers to inject malicious scripts that target active user sessions, potentially hijacking session cookies or tokens. Successful exploitation grants the attacker the same privilege level as the targeted user, including possible root access for full device control.

MitigationUpgrade Junos OS to the specified patched versions for each affected release train. If immediate patching is not possible, disable J-Web interface or restrict access to trusted management networks only.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
JunosOperating system
Affected:= 12.3= 15.1= 12.3x48= 15.1x49= 16.1= 16.2= 17.1= 17.2= 17.3= 17.4= 18.1= 18.2

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Verify if J-Web interface is enabled
    Run 'show system services web-management' to check the web-management configuration and confirm whether J-Web is listed as active
    Affected if J-Web interface is enabled on the device (the vulnerability only applies when J-Web is active)
  2. Check installed Junos OS version
    Run 'show version' or 'request system version' to retrieve the exact Junos OS version installed on the device
    Affected if The installed version matches any of these: 12.3, 15.1, 12.3x48, 15.1x49, 16.1, 16.2, 17.1, 17.2, 17.3, 17.4, 18.1, or 18.2
  3. Review system logs for XSS indicators
    Run 'show log messages' and search for patterns such as '<script>', 'javascript:', or 'onerror=' within web-management or J-Web related entries
    Affected if Log entries contain suspicious XSS payload patterns associated with J-Web requests
  4. Audit active and recent J-Web sessions
    Run 'show system users' or check 'show log interactive-commands' for unexpected administrative logins via J-Web
    Affected if There are unauthorized J-Web sessions or suspicious session activity that does not match legitimate administrator actions

A device is affected if J-Web is enabled AND the Junos OS version matches the affected version list (12.3 through 18.2), regardless of whether exploitation is confirmed in logs.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Junos OS to the specified patched versions for each affected release train. If immediate patching is not possible, disable J-Web interface or restrict access to trusted management networks only.

Recommended fix High confidence

12.3R12-S15 (EX), 12.3X48-D95 (SRX), 15.1R7-S6 (EX), 15.1X49-D200 (SRX), or the specific patched version for other trains as listed in the advisory

  1. 1. Identify the exact Junos OS version currently running on the device using 'show version' command
  2. 2. Determine the product series (EX Series or SRX Series) and the base version train (12.3, 15.1, 16.1, etc.)
  3. 3. For EX Series on 12.3: upgrade to 12.3R12-S15 or later
  4. 4. For SRX Series on 12.3X48: upgrade to 12.3X48-D95 or later
  5. 5. For EX Series on 15.1: upgrade to 15.1R7-S6 or later
  6. 6. For SRX Series on 15.1X49: upgrade to 15.1X49-D200 or later
  7. 7. For all other versions (16.1, 16.2, 17.x, 18.x, 19.x): upgrade to the specific fixed version listed in the advisory for the respective version train
  8. 8. Download the appropriate Junos OS upgrade image from the Juniper Networks support portal
Caveat Review Juniper upgrade documentation for your specific hardware platform; some platforms may have specific upgrade considerations

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Junos Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-0275 in production — separate from our analysis above.

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What this is

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What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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